In a silver halide photographic element, a color image is formed when the element is exposed to light and then subjected to color development with an aromatic amine developer. Color development results in imagewise reduction of silver halide and production of oxidized developer. Oxidized developer then reacts with one or more incorporated dye-forming couplers to form an imagewise distribution of dye.
Color photographic materials and methods commonly employ silver halide emulsions, with silver chloride emulsions being particularly suitable in many applications. In photofinishing processes, which use photosensitive paper to produce color prints, it is generally desirable to shorten the processing time to improve productivity. One way to shorten the processing time is to accelerate the development rate by using primarily silver chloride emulsions.
The continuing thrust towards digital printing of photographic color papers has created the need for a consumer color paper that can work in both optical and digital exposure equipment. Ideally, a color paper that could substantially maintain tone scale from conventional optical negative working exposure times to sub microsecond digital direct writing exposure times would be preferred. This would enable a photofinishing area to maintain one paper for both digital and optical exposure thereby reducing the need for expensive inventory.
There is also a continuing need to reduce costs associated with the manufacturing of color print media, as well as a need to improve the ease of manufacture. One way to reduce cost is to reduce the level of silver per unit area of media. Another way is to reduce the level of expensive chemicals, such as color-forming coupler compounds. However, when these approaches are attempted, often the resulting photographic prints obtained have poor color, and the resulting color reproduction is unacceptable. Another problem often observed when silver and coupler levels are reduced is a problem termed fringing. Fringing can occur when the print medium is given a digital exposure (high intensity for a short period of time). It is a color aberration with respect to text and lines in the image; the text and lines appear to have a “fringe” of color. The fringing problem also limits the amount that silver that can be reduced to adjust the curve shape of the photographic media during manufacturing process, making the media more difficult to manufacture.
Typical photographic color print media include a multilayer structure having three light sensitive silver halide image recording layers, as well as other non-light sensitive interlayers. The image recording layers typically comprise silver halide and a dye-forming coupler. Commonly, the print media includes three color records, which correspond to three layers in which the silver halide is sensitive to red, green, and blue light respectively and contain cyan, magenta, and yellow dye-forming couplers respectively. During photographic processing the silver halide reacts with developer to form oxidized developer (Dox) that undergoes further reaction with coupler to produce image dye, preferably in the same image-recording layer in which the Dox is formed. Because Dox can migrate to other layers in the structure, it is possible for it to react with the wrong coupler and form unwanted dye. The term “chemical cross talk” refers to the formation of unwanted dye caused by migration of oxidized developer from one image recording layer to another.
One aspect of interimage, that is, the effect of one layer on another, in photographic paper relates to the propensity of chemical cross talk occurring during development. Papers with high interimage show degraded color reproduction and have a more restricted color gamut (range of accessible colors) relative to a paper having low interimage that produces the same image dyes. To control cross talk, image recording layers are surrounded by non-light sensitive interlayers that contain reactive chemicals known in the trade as “scavengers”. Scavengers are organic compounds that convert oxidized developer back to developer, or a noncolored by-product, before the oxidized developer can migrate to an adjacent color record and form unwanted dye. Scavengers are typically organic reducing agents, including but not limited to, compounds known in the trade as hydroquinones and their derivatives. For example, see R. W. G. Hunt, The Reproduction of Color in Photography, Printing and Television, 4th Edition, Copyright 1987, Fountain Press, Chapter 8, Plate 10, which describes the structure of conventional color paper and shows the interlayers separating the three dye-forming image layers and U.S. Pat. No. 5,744,287 teaches preferred dye characteristic curves for a conventional paper in a sub-50 microsecond exposure.
Lower contrast toe regions of the paper H&D, also known in the art as D-log E or D-log H, curves can alleviate contouring. Kokai JP 05/142712-A of Kawai teaches the preferred toe shape of the characteristic dye curve in a scanning exposure employing 10-bit modulation.
A limitation of organic reducing agents as interlayer scavengers is their reactivity with image dye after photographic processing. Because scavengers are retained in the coating after processing, conditions that promote diffusion of the scavenger into a dye-containing layer may lead to dye destruction due to reaction of the scavenger with the dye to form colorless by-products. Common surface treatments, such as embossing, promote the migration of scavengers into image layers by subjecting prints to localized high pressure (˜5000 psi). Treatment of the surface with organic solvents can have the same effect.
Another limitation relates to the migration of scavenger into the dye-forming layers prior to photographic processing. In this case, the scavenger may compete for Dox with dye-forming coupler and cause less efficient dye formation, resulting in loss of desired density and/or contrast. In particular, dispersions of magenta dye-forming couplers derived from pyrazoletriazoles are susceptible to scavenger competition. Neutral flat fields that develop to a more green looking neutral at the slit edge of a coating illustrate this problem. The cutting knives may subject the coating to enough local stress to force the scavenger into the magenta dye-forming layer, causing this layer to develop to a lower density on the edge of the coating.
Scavengers also interfere with the light stability of the image dyes either by direct reaction with the dye when exposed to light, or by reaction with other components such as UV dyes and chemical stabilizers that are coated with photographic couplers to protect the image dyes from exposure to light. Destruction of the UV dyes or stabilizers enhances the rate of fade of the image dye.
Scavengers also limit the inherent chemical efficiency of a photographic system because Dox is lost to reactions that produce no image dye. Raising the level of silver to compensate for the loss of Dox can lead to increased chemical cross talk and process sensitivity. More efficient conversion of Dox to image dye permits lower silver lay downs and shorter development times for a given density.
These problems have been described in detail in U.S. Pat. No. 5,736,303, which teaches the preferred ratio of gel to organic component in the coating layers to minimize scavenger migration. It would be more preferred, however, to reduce the level of scavengers in the interlayers while retaining suitable color quality for both optical and digital exposures.
U.S. Pat. Nos. 6,312,880; 6,280,916; and 6,268,116, incorporated herein by reference in their entirety, describe a multilayer photographic element including light sensitive layers and non-light sensitive dye-forming interlayers wherein each interlayer is completely or substantially scavenger free. This approach may alleviate many of the problems associated with high scavenger levels, however, scavenger compounds are relative low molecular weight, simple molecules while coupler compounds tend to be high molecular weight, complex and expensive chemicals. Although this approach has the advantage of essentially eliminating the scavenger, it has the undesirable effect of replacing the relatively inexpensive scavenger chemicals with expensive couplers. Thus, this is not a practical approach that would provide economical photographic materials.